Helicopter single-blade rotor

ABSTRACT

The present invention relates to a single-blade main rotor for helicopters designed so that the component of the blade lift normal to the rotational axis of the rotor is compensated by the inertial force obtained through the self-adjustment of the position of the rotor centre of mass relative to its rotation axis, it being provided that the position of the rotor centre of mass is determined by the coning angle of the blade.

The present patent application for industrial invention relates to asingle-blade rotor designed to be used as main rotor in helicopters andother types of rotorcraft. The rotor supports the helicopter duringhovering and translated flight and, by means of its controls, allowsexecution of the manoeuvres typical of this type of vehicle.

To this end, helicopters are usually equipped with vertical axis rotorsprovided with two or more identical blades joined by hinges or similarmeans to a central propeller hub, which is in turn fixed to the upperend of a vertical mast driven by a system for the transmission of therotary motion connected to one or more engines.

When maintained in rotation at the appropriate speed, the blades supportthe helicopter because of the upward lift produced as a consequence ofthe relative air speed with respect to the aerodynamically profiledblades. Moreover, the blades are subject to the weight force and, due torotation, to the centrifugal force. The balance of all these forces andtheir moments with respect to the joints of the blades to the rotor huband the mast, to which the weight of the rotorcraft is applied,determines the geometrical position of the blades, which, with respectto the plane orthogonal to the rotation axis, are directed upwards witha normally small coning angle. The entity of the total lift is adjustedby the pilot through the collective control lever that acts on the bladepitch by means of rods, levers, and rotating mechanisms connected withsuitable pitch horns located on the hub of each blade, coupled in arotary way to the rotor hub, with rotation axis sensibly parallel to itsown longitudinal axis.

The control mechanisms allow the pilot to change the pitch of each bladewith the cyclic control lever, with respect to the average valuedetermined by the collective control, in order to create pitchdifferences symmetrical to this average value, in positionsdiametrically opposed to the rotational axis, inducing the rotor disk totilt, thus causing the helicopter to move in the corresponding directionof tilting.

Rotors are usually manufactured according to multiple solutions, all ofwhich, in order to guarantee correct operation, require the blades to beidentical in terms of entity and mass distribution and as similar aspossible in terms of shape and aerodynamic behaviour, while the jointsat the rotor head and the kinematic chain that controls their pitch musthave the same characteristics for all the blades of the rotor.Therefore, in order to maintain acceptable performance, such rotorsrequire frequent maintenance works of blades tracking and balance,involving complicated procedures and methods and using specialequipment.

In such multi-blade rotors, the lifting surface is divided between theblades of the rotor. With the same diameter and solidity, in amultiblade rotor each blade has a shorter mean chord which, for a givenrotor tip, results in a lower value of the ratio between the product ofthe speed multiplied by the chord and the kinematic viscosity of the air(Reynolds Number). Since this lower value results in an increased bladedrag coefficient for a given lift, it is therefore convenient to reducethe number of blades.

Moreover, it must be stressed that the rotation of each lifting bladeproduces a wake that can disturb the following blade, especially duringhovering or low speed flight, with negative effects on its performance.The time interval between the passage of one blade in a disk area andthe following as the number of rotor blades decreases, under givenconditions, thus reducing the perturbation of the air in which the rotoroperates.

In view of the above considerations, whenever possible, the adoption ofa reduced number of blades can give aerodynamic advantages over similarrotors with a higher number of blades. Moreover, the reduction in thenumber of blades decreases the number of components and moving parts,leading to the simple bi-blade rotor with suspended hub connected to themast with a horizontal hinge normal to the rotation axis.

Experiments have also been carried out with single-blade rotors in whichthe blade is balanced by a counterweight, but the difficulties inobtaining an acceptable balance between the forces and moments acting onsuch rotors under various operating conditions have not allowed theapplication and diffusion of such solutions.

The main purpose of the present invention is to overcome theinconveniences found in multi-blade and single-blade helicopters ofknown type, by means of a main rotor system for helicopters consistingof a single blade with central hub, a counterweight and balancingdevices, having high flexibility and adaptability and characterised byeasy construction, safe use and efficient operation.

The second purpose of the present invention is to create a single-bladerotor system, with working mechanism, in which the balance of the forcesand moments acting on its parts is obtained by means of the reciprocalpositions assumed by these parts as the coning angle of the single bladevaries. The mechanisms controlling rotor balancing may be kinematicsystems of known type, or other electromechanical or hydraulic devices.In any case, the horizontal component of the lift of the single blade isbalanced by an identical opposed misbalance of centrifugal inertialforces, obtained by moving the rotor centre of mass relative to itsrotation axis.

The third purpose of the present invention is to devise a rotor system,with control mechanisms, which does not require blades-tracking toensure correct operation.

Last, but not least, another aim of the present invention is to design amechanism capable of creating and maintaining a stable balance betweenthe elements of the single-blade rotor during operation.

These and other aims, which will be highlighted in the descriptionbelow, can all be achieved by the present invention.

Further characteristics and advantages of the invention will become moreevident from the following description of three different embodiments,with reference to the enclosed drawings, which are intended for purposesof illustration and not in a limiting sense, whereby:

FIG. 1 is a schematic side view of the single-blade rotor and thedevices used to maintain the balance, normal to the rotational axis ofthe rotor and the longitudinal axis of the blade according to a firstembodiment;

FIG. 2 shows the same embodiment in an exploded axonometric view;

FIG. 2A is a view of the friction devices;

FIG. 3 and 4 are the same as FIG. 1, with the rotor blade inclined at agiven coning angle;

FIG. 5 is a schematic side view of the single-blade rotor and thedevices used to maintain the balance, normal to the rotational axis ofthe rotor and the longitudinal axis of the blade according to a secondembodiment;

FIG. 6 is a schematic side view of the single-blade rotor and thedevices used to maintain the balance, normal to the rotational axis ofthe rotor and the longitudinal axis of the blade according to a thirdembodiment.

The above figures show that the hub (1) of the rotor is joined to thesupport (14) of the blade (8) and made up of a vertical pair of plates(1 a and 1 b) symmetrical to the mast (7). The blade (8) is joined tothe support (14) by a pitch hinge of known type, so that the blade canrotate around its longitudinal axis A—A, changing its geometrical pitchthrough joints and devices of known type, very similar to thosegenerally used in helicopter rotors, applied to the pitch horn (9) ofthe blade, controlled by the rod (10).

The blade (8) is also fitted with a hinge, of virtual type also, withaxis B—B in vertical and eccentric position with respect to the axis Y—Yof the mast which allows it to assume an angular position in the planeorthogonal to the rotational axis Y—Y, the said hinge being equippedwith a damper or similar known devices.

The two plates (1 a and 1 b) making up the hub (1) contain two holes (1c) on the same axis R—R in which the cylindrical body (2) is coupled ina rotary way, the said body being centrally hollow and coupled in arotary way also to the top of the mast (7) by means of a pair ofopposing pins (7 a), appropriately provided with friction devices 30,31, with axis X—X normal to the same mast. The two opposite sides of thecylindrical body (2) also house two rotating coaxial cylinders (3) withaxis T—T eccentric to the other axis R—R and X—X in a rotary way. Thecylinders (3) are housed in an opposing coaxial pair of eccentric holes(2 b) located in the aforementioned hollow body (2), which featuresanother opposing coaxial pair of holes (2 a), housing the pin (7 a)mentioned above.

These cylinders (3) are in turn connected through revolving eccentricpins (4) to two pairs of identical levers (5) of the hub (11) of thecounterweight, comprising the hub (11) placed at the end of an arm (12),featuring a profiled mass (13) at the other end.

The hub (11) is hinged in a rotary way to the rotor hub (1) by conaxichinges (6) with appropriate friction devices, normal to the longitudinalaxis of the counterweight; the joining of the centre of the pins (6)with the barycenter of the counterweight (13) determines a directionC—C. The hinges have threaded ends (6 a).

More exactly, the hinges (6) are housed in two opposite coaxial holeslocated on the plates (1 a and 1 b) of the hub (1) along an axis W—Wparallel to, but underlying, the axis X—X.

When the blade rotates without lift (FIG. 1), it rotates in almost thesame horizontal plane as the counterweight , whose axis is formed byextending the axis A—A.

When the pilot increases the geometrical pitch of the rotating bladewith the collective control, the lift inclines the blade upwards at aconing angle (β) such that the lift balances with the other forces andmoments acting on the blade (FIG. 3). When executing this movement theblade (8) drags the hub (1) to which it is joined, which rotates aroundthe axis (R—R) of the cylindrical body (2) at a corresponding angle (β).

The rotation also takes place with respect to the counterweight, whichmaintains its longitudinal axis orthogonal to the rotation axis Y′—Y′ ofthe rotor. Thanks to this relative motion, the cylinders (3) linked bythe revolving eccentric pins (4) to the levers (5) of the counterweightand the cylindrical body (2), coupled in a rotary way to the hub (1)rotate around each other, determining a new position of the hub (1)relative to the rotational axis Y—Y, along the direction C—C, passingthrough X—X that is, a different position of the rotor centre of masswith respect to the rotational axis. Since the lift is perpendicular tothe blade, the coning of the blade involves a horizontal component ofthe lift, directed towards the centre of rotation. The horizontal forcecomposes with the inertial forces affecting the blade and thecounterweight. By appropriately dimensioning the relative positions ofthe pins (4), the hinges (6) and the axes R—R, X—X, T—T using knowncalculation methods of known type and considering the masses andpositions of the relative barycentres of the blade, counterweight andthe other components of the rotor and the mutual joints, it is possible,within the normal range of coning values to set up a sufficientlyapproximate and stable balance which remains constant on variating theconing angle and is practically independent of the rotational speed ofthe rotor, since the forces that act on the rotor—whether due to lift orinertia—all proportional to the square of the rotational speed.

The pitch variations, caused by the pilot acting on of the cycliccontrol from the pilot or determined by the asymmetry of the air flowinvesting the blade during horizontal flight, cause the rotational planeof the counterweight to tilt, with consequent tilting of the entirerotor around the axis X—X, as illustrated in FIG. 4, thus allowing thehelicopter to be moved and controlled.

FIG. 5 illustrates a second embodiment—but not last—of the presentinvention in which the displacement of the rotor centre of mass relativeto the rotational axis Y′—Y′ and along the direction C—C, in order tobalance the horizontal component of the lift, is carried out by anelectromechanical actuator (15) acting between pins (16) and (17),respectively joined to the hub (1) of the rotor and the cylindrical body(2), which is in turn coupled in a rotary way with the hub, electricallycontrolled by a control box (18) according to the value detected andtransmitted with electrical signals by the telescopic detection device(19) of known type of the relative distance assumed by the points (20)and (21), in relation to which the detector (19) is respectively hingedto the hub (11) of the counterweight and the hub (1) of the rotor, asthe coning of the blade (8) changes.

In fact, the control box is designed and programmed using knowncalculation methods and construction systems, so that for each coningvalue of the blade, as measured by the detector device (19), theactuator (15) causes the cylindrical body (2) to rotate around the hub(1) so that the rotor centre of mass relative to the rotation axis,passing through X—X, assumes the correct position to ensure balancebetween the aerodynamic and inertial forces acting on the rotor.

FIG. 6 illustrates a third embodiment of the present invention, in whichthe actuator (15) controlled by the control box (18) radially displacesthe mobile mass (22) that slides on the rod (12) of the counterweight,according to the coning angle measured by detector (19), thus changingthe position of the rotor centre of mass relative to the rotational axisof the rotor.

The actuator (15) is joined by hinging pins (16 and 16 a) to one of theplates of the hub (1) and to the mobile mass (22).

In this construction version the two plates of the hub (1) only show twoopposing holes (23) located along the same axis X—X perpendicular to therotational axis Y—Y of the rotor. The holes (23) house the pins (7 a)located at the top of the mast (7).

What is claimed is:
 1. Single-blade rotor for helicopters of the typecomprising: a mast (7) with vertical rotation axis Y—Y provided with anopposing coaxial pair of pins (7 a) along an axis X—X, orthogonal to therotation axis Y—Y; the mast (7) having a top: a hub (1) of the rotorjoined to the mast (7) and provided with a support (14) for a blade (8);a single blade (8)—operated by conventional means (10) connected to asuitable lever (9) of the blade (8)—joined to the support (14) by apitch hinge that allows small rotations around the blade's longitudinalaxis A—A; a counterweight (13) made up of a profiled mass located at oneend of an arm (12) which terminates, at the other end of the same arm,with a hub (11) of the counterweight (13) used to hinge the saidcounterweight to the hub (1) of the rotor, wherein said rotor rotatesaround an axis Y′—Y′; pins (6) for hinging the hub (11) of thecounterweight (13) to the hub (1) of the rotor, wherein the joining ofthe centre of the pins (6) with the centre of mass of the counterweight(13) determines a direction C—C. characterized by the fact that: a) thehub (1) of the rotor can rotate around the axis X—X; b) the hub (11) ofthe counterweight (13) is hinged to the hub (1) of the rotor with thepossibility of oscillation, with friction, around an axis W—W parallelto the axis X—X, underlying it; c) the inclination of the hub (1) of therotor around the axis X—X—caused by a variation of the blade's coningangle β—does not determine the corresponding inclination of thecounterweight (13), whose rotation plane remains orthogonal to therotation axis Y′—Y′ of the rotor; d) means for causing the displacementof the rotor centre of mass with respect to the rotation axis Y′—Y′ andalong the direction C—C according to the inclination of the hub (1) ofthe rotor around the axis X—X with subsequent balance of the liftcomponent—normal to the rotation axis of the rotor Y′—Y′—of the blade(8) and the inertial forces; e) friction devices positioned between thehub (1) of the rotor and the hub (11) of the counterweight (13) assurethat the inclination of the rotation plane of the blade (8) around theaxis X—X—caused by a cyclic variation of the pitch of the blade(8)—determines a simultaneous corresponding inclination of the rotationplane of the counterweight (13), with subsequent inclination of therotation axis Y′—Y′ of the rotor.
 2. Single-blade rotor for helicopters,according to claim 1, characterized by the fact that the means fordisplacement of the rotor centre of mass with respect to the rotationaxis Y′—Y′ comprise a cylindrical body (2) having a longitudinal axisR—R parallel to the axis X—X; said cylindrical body (2) is housed in thehub (1) of the rotor and is free to rotate around the axis X—X andfeatures a deep hollow, into which the top of the mast (7) is inserted,and an opposing coaxial pair of pins (7 a) housed in two correspondingeccentric holes (2 a) of the cylindrical body (2); means being providedthat determine the rotation of the cylindrical body (2) inside the hub(1) of the rotor and around the axis W—W with subsequent displacement ofthe rotor centre of mass along the direction C—C.
 3. Single-blade rotorfor helicopters, according to claim 2, characterized in that the mansthat determine the rotation of the cylindrical body (2) inside the hub(1) of the rotor and around the axis W—W comprise: revolving cylinders(3) housed in an opposing coaxial second pair of eccentric holes (2 b)located on the cylindrical body (2); levers (5) located on the hub (11)of the counterweight (13) and fixed to the cylinders (3) by means ofeccentric pins (4); the pins (6) for hinging the hub (11) of thecounterweight (13) to the hub (1) of the rotor.
 4. Single-blade rotorfor helicopters, according to claim 2, characterized in that the meansthat determine the rotation of the cylindrical body (2) inside the hub(1) of the rotor and around the axis W—W comprise: an electromechanicalactuaor (15) having actual movements and having hinging pins (16 and 17)respectively joined to the hub (1) of the rotor and to the cylindricalbody (2); a telescopic device for linear detection (19) being hinged atone end (21) to the hub (1) of the rotor and at the other end, to thehub (11) of the counterweight (13) the hinging pin at the end (20) ofthe telescopic device is eccentric with respect to the hinging pin ofthe hub (11) of the counterweight (13); a control box (18) that controlsthe actuator (15) according to the distance between the two oppositeends (20 and 21) of the telescopic device (19) distance which isdetected and transmitted by the telescopic device (19) itself; whereinan upwards inclination of the hub (1) of the rotor—determined by thelift of the blade (8)—around the axis X—X and with respect to thecounterweight (13), causes a variation of the distance between the twoopposite ends (20 and 21) of the telescopic device (19); said variation,by means of the control box (18), determines corresponding displacementsof the hinging pin (17) of the actuator (15) with respect to the hingingpin (16) of the actuator (15) and subsequent rotations of thecylindrical body (2) that cause the displacement of the rotor centre ofmass relative to the rotation axis Y′—Y′ of the rotor; the control box(18) is made—such that a univocal angular position of the cylindricalbody (2) determined by the actuator (15) that operates the variation ofthe distance between the hinging pins (16 and 17) of the actuator (15)corresponds to each value of the coning angle β.
 5. Single-blade mainrotor for helicopters, according to claim 1, characterized in that themeans provided to cause displacement of the rotor centre of mass withrespect to rotation axis Y′—Y′ comprise: a mobile mass (22) that slideson the arm (12) of the counterweight (13); an electromechanical actuator(15) having axial movement and, having hinging pins (16 and 16 a)respectively joined to the hub (1) of the rotor and to the mobile mass(22); a telescopic device for linear detection (19) being hinged at oneend (21) to the hub (1) of the rotor and at the other end to the hub(11) of the counterweight (13) the hinging pin at the end (20) of thetelescopic device (19) is eccentric with respect to the hinging pin ofthe hub (11) of the counterweight (13); a control box (18), thatcontrols the actuator (15) according to the distance between the twoopposite ends (20 and 21) of the telescopic device (19), distance whichis detected and transmitted by the telescopic device (19) itself;wherein an upwards inclination of the hub (1) of the rotor—determined bythe lift of the blade (8)—around the axis X—X and with respect to thecounterweight (13), causes a relative displacement between the twoopposite ends (20 and 21) of the telescopic device (19) that, by meansof the control box (18), determines corresponding displacements of thehinging pins (16 and 16 a) of the actuator (15) with subsequentdisplacement of the mobile mass (22) and of the rotor centre of masswith respect to the rotation axis Y′—Y′ of the rotor.
 6. Single-bladerotor for helicopters, according to claim 2 characterized in that thehub (1) of the rotor is composed of an opposing pair of symmetricalplates (1 a and 1 b)—joined to each other by the support (14)—featuringone opposing pair of holes (1 c) and a second opposing pair of holes (1d), where the first pair of holes (1 c) houses the cylindrical body (2),while the second pair of holes (1 d) houses the hinging pins (6) of thehub (11) of the counterweight (13).